all signs on the motorways should be lit by this means. We do not consider that lighting of these signs from the top alone, as is customary with signs of smaller size, would be adequate, because the illumination cannot, with such large signs, be made sufficiently uniform, a factor which we regard as important.
26. Some of the largest signs on the Preston By-Pass are illuminated by experimental floodlights constructed to the design of the Road Research Laboratory.[1] They are mounted in reflectors arranged across the width of the sign, a short distance in front of it and just below its lower edge, and the profile of the reflector has been designed to give uniform illumination over signs of varying heights. This system of lighting gives satisfactory results, but it will be necessary to keep the fittings as small as possible in relation to the sign to ensure that they do not spoil the appearance of the sign or reduce its effectiveness.
27. We have noticed that, to help good illumination of the top of a tall sign from electric lighting at the bottom, a horizontal reflecting strip, having an overhang of about nine inches, is placed across the top of the sign. In daytime this strip can cast a shadow over the upper part of the sign. It must be seen to that this is not allowed to obscure the message.
28. The floodlighting units at Preston were coloured to match the blue of the face of the sign, and this seriously distracted attention from the sign itself. We recommend that floodlighting equipment should be the same neutral colour as the backs of the signs (see paragraph 24 above).
29. Where electric lighting is impracticable we recommend the use of reflective sheeting of good quality[2] on the letters, symbols and borders of the signs. The slight loss of contrast which results in daylight from the fact that some of these materials are not pure white does not seem to us to be serious, although we look forward to a time when a real white can be achieved.
30. When we inspected the experimental signs on the Preston By-Pass we noted that the performance of reflectorised signs in the full light of headlamps was excellent, but that there was a substantial loss of performance with dipped lights.[3] Having regard to the present regrettable need to use dipped lights in the face of oncoming traffic on the motorway, and to the fact that on a three-lane carriageway the signs, on the left of the hard shoulder, are even further to the side of the fastest traffic than they are at Preston, we consider the use of reflecting material to be very much a second best alternative as compared with electric lighting.
Mounting and Siting
31. Since the signs on the Preston By-Pass were experimental they were mounted on frankly temporary tubular frames which have been criticised as unsightly. We have been shown two alternative forms of permanent support, comprising
- ↑ V. J. Jehu: 'A method of illuminating direction signs on motorways' (Light and Lighting, 1959, 51(11), 339-40).
- ↑ As specified in British Standards Specification 873 of 1959.
- ↑ From American data and from the results of tests carried out in this country, the reduction is estimated at about 10-20 per cent for 12-inch letters.
7
